Messages in this thread | | | Date | Sat, 20 Jun 1998 00:41:55 +0200 (MET DST) | From | Davide Rossetti <> | Subject | Re: RAID0 poor performances |
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On Fri, 19 Jun 1998, Hubert Tonneau wrote:
> I know nothing about MD, but i would not say that 10Mb/s is poor. > > As a comparison, on my single SCSI disk drive, i get 3Mb/s (the > disks are not very new, i admit, but they are still Fast SCSI 2 > linked to a PCI controler) > > According to me, 5Mb/s is a resonable performance for a single > disk, so 10Mb per seconds for 2 disks sounds fine.
they are four!
> About your test report, i was surprised to see the line: > Ultra SCSI: Disabled > If you want top performances, you probably need Ultra SCSI bus > (20 Mb/S if narrow, 40 Mb if wild) > since 2 disks require twice more bandwild on the SCSI bus that > a single one.
the theory is: ok 1 disk <= 8 MB/s --> 2 disks could use a 16MB/s bandwidth, well under 20 MB/s peak SCSI2-wide bandwidth. I use TWO controllers, each one driving TWO disks, so I have a 4 disks striping setup.
> Ok the Adaptec controler as two SCSI bus: did you verify that > the two disks that are linked in each grap are liked to a > different SCSI bus.
they are 2 different controller boards !! I you look at the URL I referenced, you can see the complete setup. It would be really useful.
Anyway, looking at the md driver source code, that moderate speed-up is ok as there is (it seems to me) no I/O overlapping between different disks accesses. ie. when a block write operation is dispatched to a disks, it is someway waited for completion (ok, not properly, but I tested with 250-500 MB write operations, so caching sould have no effect; moreover it is a waste of cycles).
regards.
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